1. Field of the Invention
This invention relates to a copolymer for the manufacture of chemical amplified photoresist and a positive photoresist composition containing the copolymer and more particularly, to the chemical photoresist composition which can provide several advantages: a) ultrafine patterns can be formed irrespective of any substrate, b) a higher alkali-soluble contrast can be ensured before and after exposure, c) a larger scope of exposure can be obtained, and d) a variety of excellent physical properties such as sensitivity, resolution, heat-resistance and stability after exposure. In particular, the chemical amplified positive photoresist composition of this invention can be used as ultrafine patterns-forming material for ultra-LSI which can be sensitive to UV light, far ultraviolet ray, excimer laser, X-ray and electron beam.
2. Description of the Related Art
The recent semiconductor technology has been briskly in favor of more highly integrated chip and in parallel with this trend, ultrafine patterns having less than quarter-micron are required in the photolithography patterning designed to prepare an ultra-LSI. In this respect, since the exposure wavelength becomes more short in the conventional g-ray or i-ray, the research and development project for far ultraviolet ray, KrF excimer laser, X-ray and electron beam lithograph has drawn keen attention in the related field.
A photoresist used in the conventional g-ray or i-ray employs some Novolac-quinonediazide compounds. Since such photoresist applied to the wavelength of far ultraviolet ray or KrF excimer laser absorbs a lot of light, intensive researches have focused on a chemical amplified photoresist using polyhydroxystyrene derivatives which absorb less light than these Novolac-quinonediazide compounds.
The major principle of such chemical amplified photoresist composition is that the resist layer is exposed in patterns by chemical ray, some acid generator contained in the photoresist composition releases an acid which in turn triggers an catalytically active deprotection with a resin composition, thus changing the solubility to a developer solution.
In particular, since the chemical amplified photoresist composition may demonstrate an excellent catalytic activity on resin composition in the presence of a small amount of acid generated from an acid generator, its higher resolution in patterns and better sensibility on chemical ray may be ensured.
The examples of such chemical amplified photoresist material include poly(p-t-butoxycarbonyloxystyrene/p-hydroxystyrene; U.S. Pat. No. 4,491,628), poly(p-t-butoxystyrene/p-hydroxystyrene; U.S. Pat. No. 5,350,660) and poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene, Japanese Patent No. A-5-249682).
However, if some protecting groups of base resin in the photoresist material are tert-butyl group or tert-butoxycarbonyl group, they are decomposed in strong acid which in turn becomes inactivated via reaction with basic compounds in the air. The resist material is liable to form a T-top, while having different patterns according to the types of substrate. Meantime, in case of some base resins having protective groups which are decomposed in weak acids such as acetal group or ketal group, their basic compounds are less affected in the air but the formation of patterns will be extremely narrowed due to time-relapse delay from exposure to radiation to thermal treatment (PEB), while being unsuitable for higher resolution.